This invention relates to a direct injected, internal combustion engine and more particularly to an improved combustion chamber configuration for such engines.
In the interest of improving engine performance both in the terms of power output, fuel economy and exhaust emission control, it has been proposed to employ direct cylinder fuel injection. Fuel injection, per se, offers greater control over the amount of fuel introduced into the combustion chamber on each cycle of operation. By exercising such greater control, it is possible to adjust the amount of fuel injected on a cycle-by-cycle and cylinder-by-cylinder basis to improve engine economy and emission control.
Even additional improvements and performance can be obtained if direct cylinder injection is employed. If the fuel is injected directly into the cylinder and can be stratified under at least some running conditions, then substantial improvements in fuel economy and exhaust emission control can be achieved. Particularly this is very effective in reducing the emission of unburned hydrocarbons (HC).
The term "stratification" refers to the formation of a non-homogeneous fuel air mixture in the combustion chamber. If the entire combustion chamber is filled with a homogeneous mixture and one which is stoichiometric, then more fuel will be present in the combustion chamber than necessary to obtain the requisite power under most engine running conditions. This obviously gives high HC emissions under less than full load running. Therefore, if a stoichiometric patch can be formed in the combustion chamber and located so that it can be ignited at the appropriate time, it will be unnecessary to completely fill the combustion chamber with a homogeneous mixture. This presents obvious advantages in both fuel economy and exhaust emission control.
However, the condition in the combustion chamber is such that it is difficult to ensure that a stoichiometric patch will be located at the spark plug at the time of ignition, particularly under light loads or even at idle. The reasons for this is that there is motion that occurs within the combustion chamber regardless of the configuration of the combustion chamber and the porting arrangement which serves it. This air motion within the combustion chamber causes the fuel patch not only to move but also to disperse. Thus, it has been very difficult if not impossible to obtain stratification in an open combustion chamber.
Of course, if small, pre-combustion chambers are employed then a stratified, stoichiometric charge can be introduced into this restricted pre-combustion chamber and fired by a spark plug position therein. However, the use of such pre-chambers causes pumping losses which can adversely affect engine performance, particularly at higher speeds and higher loads.
A wide variety of types of combustion chambers have been proposed so as to achieve open cylinder stratification. These combustion chambers normally use bowls that are formed in the head of the piston and into which the fuel is introduced. If the spark plug is positioned so that its gap extends into the bowl the thought it that there will be a homogeneous stoichiometric mixture present at spark gap at the time of firing. However, in practice this result is not always easy to obtain.
Therefore, various bowl formations have been proposed some of which include, in addition to a main bowl, a pocket or recess in an area of the bowl into which the spark gap extends. With conventional center gaped spark plugs, where the spark gap extends axially in the cylinder, this means that the spark gap will be exposed to the interior of the pocket. By then causing the fuel mixture to accumulate in the pocket stratification can be achieved and firing improved theoretically.
There are, however, particular problems within ensuring that these combustion chambers will operate satisfactorily under all engine running conditions. Also, by extending the spark plug into the bottom of the bowl there is a risk that under certain conditions the side spark terminal may be struck by the piston and close the gap rendering further running impossible. Also the side terminal shields the center terminal and gap from the fuel/air patch.
It is, therefore, a principal object of this invention to provide an improved combustion chamber for a direct injected engine wherein stratification can be achieved and wherein extended gaps for the spark plugs are not required.
It is a further object of this invention to provide an improved configuration for a combustion chamber that embodies a bowl in the piston and which cooperates with the spark plug so that the bowl directs the flow of fuel toward the spark gap upon the compression stroke to ensure the presence of a stoichiometric mixture in an open gap at the time of firing.